In vehicle fuel systems, an electrically driven fuel pump is mounted in a fuel reservoir which, in turn, is located in the main vehicle fuel tank. The pump has an outlet leading to a fuel rail which distributes operating fuel to fuel injection units in a fuel rail at the engine. In some fuel systems, the pump has a capacity greater than that required by the engine and a pressure relief valve discharges over-capacity fuel to a return line which dumps into the reservoir.
Some systems have provided for over flow of fuel from the reservoir to the main tank. However, the reservoir fuel may be hot due to the return flow and it is not desirable that hot fuel reach the main tank. Also, it is desirable that the reservoir be closed at the top to create a back pressure and accordingly increase the pressure at the main fuel inlet to provide a force feed to the main pump.
Two-stage pumps are known and the present invention contemplates the use of a two-stage power driven pump in connecting with a fuel reservoir. A turbine vane pump is disclosed in U.S. Pat. No. 5,265,997 (Nov. 30, 1993) and also in U.S. Pat. No. 5,257,916 (Nov. 2, 1992) issued to C. H. Tuckey and the assignee common to this application. A two-stage pump is described in a German patent to Volkswagenwerk, No. 3532349 dated Mar. 27, 1986, and a Pierburg publication illustrates a two-stage pump utilizing two separate axially spaced rotors: a first rotor to deliver fuel from a main fuel tank to a reservoir, and a second rotor to deliver fuel from a reservoir to a main pump outlet.